This invention relates to foam formulations having both blast-suppressant and decontamination capabilities.
Improvised explosive devices (IEDS) represent an increasingly dangerous threat to society, particularly when they contain a toxic chemical/biological (CB) agent. It is vital that both the blast effects (a compression or pressure wave, heat and shrapnel) and the CB agent and aerosols, released from the initiation of such devices, are contained. Once released, CB agents also present a decontamination problem when deposited on the surfaces of various equipment and vehicles, or spilled on the ground.
In the last decade, patents and papers have been published on the use of foam for blast suppression. For example, in U.S. Pat. Nos. 4,541,947 and 4,589,341 to Clark et al., an improved method for blast suppression is disclosed which utilizes fire fighting foams confined in a structural barrier surrounding the blast source. Typically, water-detergent based foams are used, having an expansion 50:1-1000:1. Clark discloses the use of JET-X, from Rockwell Systems Corporation and having 1-6% detergent, containing protein additives and used in the ratio of 1-3 parts by volume for each 100 parts of water. The key to this invention is the methodology for containing a high expansion foam in a desired location.
U.S. Pat. No. 4,964,329 assigned to Broken Hill Ltd. describes a foam composition consisting of a mixture of foamable liquid and a particulate additive to be supported as a dispersion in the foam. The dispersion is claimed to be effective in sound attenuation and shock wave attenuation.
U.S. Pat. No. 4, 442,018 to P. Rand describes a foaming composition which has decreased solution viscosity for high expansion foam capability and decreased liquid drainage. Such a composition comprises a combination of a water soluble polymer of the polyacrylic acid type, a foam stabilizer of dodecyl alcohol, a surfactant, and a solvent. A key is the combination of the stabilizer and polymer used.
A very interesting U.S. Pat. No. 5,434,192 to Thach et al. describes a composition of surfactants and stabilizers consisting of a mixture of modified natural and synthetic polymer and solvents capable of producing foam viable for 12 hours to several days at 75-105 degrees F. Such foam is used to suppress the emission of volatile gases and vapors.
As described in Clark, a blast may be suppressed using foam contained in a barrier. Applicants initially conducted blast tests with a foam product known as aqueous film forming foam (AFFF)xe2x80x94initially designed for knocking down fire. The AFFF was contained in nylon dome tents that were deployed around the blast threat. The blast suppression results were very inconsistent; the foam would break down very quickly and varied from a watery form to very light and airy. The lessons learned during this phase included the realization that the physical form of the foam could be varied considerably by the foam-dispensing rate, the percentage of surfactant in the composition and the foam-dispensing nozzle characteristics. This work led to the development of a containment system described in Applicant""s co-pending U.S. application Ser. No. 60/069,533, filed Dec. 12, 1997. That system includes a tent-like enclosure that is deployed over an IED and is filled with an air-aspirated aqueous foam material deemed a Dispersal Suppressant Foam (DSF). When the IED was then detonated, the resulting shrapnel was contained within the enclosure. The foam material used comprised a product sold under the trademark of SILVEX as described by U.S. Pat. No. 4,770,794 to Cundasawmy, which issued on Sep. 13, 1988.
The inclusion of chemical (CW) and biological (BW) warfare agents (collectively CB agents) or radioactive materials into IED""s presents an even greater challenge. Not only must the blast be contained, the agents present in the IED must be effectively neutralized within the area of containment to allow personnel access to the site following activation.
Generally, decontamination of radioactive particles is not possible due to their nuclear origin, however, removal by encapsulation significantly reduces aerosolization potential. Decontamination of chemical and biological agents usually occurs by oxidation, reduction or hydrolysis. Ideally a broad spectrum decontaminant, which does not produce toxic by-products in its mode of action on any of the likely contaminants, is of greatest use when the nature of the warfare agent is unknown.
Ideally, the blast suppression and decontamination should be a result of a single process, increasing the efficiency of the operation and allowing access to the site as quickly as possible. Further, vital evidence contained within the suppression zone should not be damaged by either the suppressant foam or by the decontaminating agent.
In order to provide a single step suppression/decontamination foam, decontaminant must be included as a part of the foam formulation. While foam for blast suppression is currently available, as are decontaminants, it is not merely an obvious step to mix them together for the combined purpose of blast suppression and decontamination.
A prior art decontaminant, German Emulsion (C8), was designed to be of low corrosivity, dissolve thickeners and penetrate paint to react with embedded agents in a emulsion formulation. It was discovered however, that the emulsion or foam was somewhat unreliable and sometimes did not form at all. Such decontaminant foams would not be suitable for blast suppression for a period of time after generation.
Any inclusion of ingredients into a foam formulation must be carefully assessed to determine their effect on the bubble size and uniformity within the foam. Further, the new formulation must possess sufficient stability, as indicated by low liquid drainage rates and an acceptable expansion ratio, to continue to provide optimum blast suppression.
As discussed in U.S. Pat. No. 4,442,018 to Rand, the choice of solvent in a foam formulation can have dramatic effects on the solution viscosity and liquid drainage from the foam. Thus, solvents and co-solvents present in decontamination formulations can act effectively as de-foamers if incompatible with the foam formulation. Particulates or oxidizing components present in decontamination formulations may also have significant detrimental effects on foam characteristics.
It remains the challenge to provide an all-in-one, blast suppression and decontamination foam that combines optimum blast suppression characteristics, such as uniform bubble size, slow drainage, vertical cling, vapor suppression and low toxicity and corrosivity, with optimum broad spectrum decontamination characteristics such as solubilization and emulsification of contaminants, rapid and complete degradation of chemical and biological warfare agents to non-toxic products and low toxicity and corrosivity.
The present invention discloses the discovery that a foam formulation exists which is suitable for both blast suppressing and decontamination, particularly desirable when faced with an explosive device which has been rigged with a contaminant for destructive dissemination. In the known cases of blast suppression, a contaminant can be shown to be substantially contained by a foam, but the used foam becomes heavily contaminated.
Accordingly, a serendipitous foam formulation is provided, combining both the advantages of blast suppression and chemical and biological agent decontamination.
A foam formulation which is compatible with a decontaminant includes the following compositions:
for the surfactant, [RnH2n+1(OCH2CH2)mSO42xe2x88x92M], where R is an alkyl group having from eight to fourteen carbon atoms, m is an integer from 1 to 3, and M is Na+ or NH4+, in mixture with CH3(CH2)nCHxe2x95x90CHCH2SO3Na,
for the co-solvent, HO(CH2(CH3)CHO)nH (PPG of MW about 425) where n=5-49 and most preferably 7; and
for the foam stabilizer, Rxe2x80x94OH where Rxe2x95x90C10-C14.
The decontamination components compatible with the above foamer include hydrated chloroisocyanuric acid salts, preferably chloroisocyanuric acid is selected from the group consisting of an alkali metal of monochloroisocyanuric acid, dichloroisocyanuric acid, and a combination thereof with cyanuric acid. A preferred alkali metal of dichloroisocyanuric acid is sodium dichloroisocyanurate.
Accordingly, a preferred decontamination formulation suitable also for blast suppression comprises:
about 1% to 6% by weight and preferably from about 1% to about 3% by weight of hydrated chloroisocyanuric acid salts and more preferably lithium hypochlorite in a ratio of 5-10% of the chloroisocyanuric acid salts;
about 1% and optionally up to 8% of a co-solvent selected from the group consisting of polypropylene glycols, polyethylene glycols, and derivatives and mixtures thereof;
from about 1% to about 5% of a surfactant;
a buffer system to initially maintain said formulation at a pH from about 8.5 to about 11 for a minimum of 30 minutes and preferably initially, from about 10 to about 11; and
the balance being water.
In the preferred formulation, the foamer components have a preferred composition of
about 15 w/v % of the sodium salt of an ether sulphate of the formula CH3(CH2)11(OCH2CH2)3OSO3Na; 7.75 w/v % of a sodium olefin sulphonate of the formula CH3(CH2)nCHxe2x95x90CHCH2SO3Na where n=10 to 12, comprising a total of 22.75 w/v % surfactant;
about 10-25 w/v % of polypropylene glycol co-solvent of the formula H(OCH(CH3)CH2)nOH where n=5 to 9;
about 1-2.5 w/v % of an alcohol CH3(CH2)nOH where n=8 to 16 to act as a foam stabilizer; and optionally
about 0.3% by weight of the above corrosion inhibitors; and
the balance being water.
Accordingly, a novel method of handling explosive devices is now available. In a broad aspect, a method for dispersal suppression of an explosive CB contamination device comprises the steps of:
surrounding the explosive contamination device with a containment structure;
and filling the containment structure with an aerated foam comprising both, a high expansion foamer; and a foamer-compatible decontamination formulation effective on chemical and biological agents without significantly and adversely affecting the formation of foam. Preferably a foamer is prepared from a surfactant, a co-solvent selected from the group consisting of polypropylene glycol, polyethylene glycol, and derivatives and mixtures thereof, and a foam stabilizer; a decontamination formulation is prepared from a chloroisocyanuric acid salts, and a buffer to maintain said formulation at a pH from about 11 to about 8.5; mixing the foamer and decontamination formulation in water; and foaming the mixture.
In a novel combination, a system is provided for dispersal suppression of an explosive CB contamination device comprising:
a containment structure for surrounding the explosive contamination device; and
aerated foam contained within the structure being formed from a decontamination formulation in water comprising a surfactant, a foam stabilizer, a solvent selected from the group consisting of polypropylene glycol, polyethylene glycol, and derivatives and mixtures thereof, chloroisocyanuric acid salts, and a buffer to maintain said formulation at a pH from about 11 to about 8.5.
In the preferred use for surrounding an explosive device, the foam formulation in water comprises about 0.4-4 weight % of a surfactant; about 0.03-0.5 weight % of a foam stabilizer; and about 0.10-9.5 weight % of a co-solvent; about 3-6 % of the chloroisocyanuric acid salts; the buffer and the balance being water. Preferably, and still effective for decontamination and foaming capability is a formulation 0.6 weight % of the surfactant; about 0.03 weight % of the foam stabilizer; about 0.75 weight % of the co-solvent; and about 3% of the chloroisocyanuric acid salts.